Planetary gear material and heat treatment

In general, the weight of planetary gear transmission device is directly proportional to the weight of gear, while the weight of gear is closely related to its material and heat treatment hardness. For example, under the same power, the weight of carburized and quenched gear will be about 1 / 3 of that of quenched and tempered gear. Therefore, in view of the structural characteristics of planetary gear reducer and the load properties of gears, hard tooth surface gears should be widely used. There are many heat treatment methods to obtain hard gear, such as surface quenching, overall quenching, carburizing quenching, nitriding, etc., which should be selected according to the characteristics of planetary gear reducer.

1. Surface hardening

The common surface quenching methods are high frequency quenching (for small size gear) and flame quenching (for large size gear). When the surface hardened layer includes the bottom of the tooth root, the effect is the best. The commonly used material for surface hardening is steel with carbon content of about 0.35% ~ 0.5%, and the hardness of tooth surface can reach 45 ~ 55HRC.

2. Carburizing and quenching

The carburized and quenched gear has relatively maximum bearing capacity, but it must adopt the finishing process (gear grinding) to eliminate the heat treatment deformation, so as to ensure the accuracy.

The alloy steel with carbon content of 0.2% ~ 0.3% before carburizing is commonly used for carburizing and quenching gears, and the hardness of its tooth surface is usually in the range of 58% ~ 62% HRC. If it is lower than 57hrc, the strength of tooth surface will decrease significantly, and if it is higher than 62Hrc, the brittleness will increase. The hardness of the tooth center is generally 310-330hbw. The hardness of carburized and quenched gear shall be gradually reduced from the surface to the deep layer, while the effective carburizing depth is specified as the surface to the deep layer, while the effective carburizing depth is specified as the surface to the hardness of 52.5hrc.

The effect of carburizing and quenching on the bending fatigue strength of gear teeth is not only to improve the hardness of the center, but also to have the residual compressive stress on the surface, which can reduce the stress in the maximum tensile stress area of gear teeth. Therefore, when grinding the teeth, it is not allowed to grind the root part of the teeth. When hobbing, it is necessary to use a hob with reserved grinding amount.

3. Nitriding

The use of nitriding can ensure that the tooth surface hardness and wear resistance are very high under the condition of minimum deformation. After heat treatment, the final finishing can not be carried out and the bearing capacity is improved. This is of special significance for the internal gear which is not easy to grind.

4. Combination of hardness of gear to be meshed

When the big and small gears are all soft tooth surfaces, the hardness of the tooth surface of the small gear should be higher than that of the big gear. When the two wheels are hard tooth surfaces and the hardness is high, the hardness of the two wheels is the same.

Choosing the right material of planetary gear reducer is beneficial to improve the bearing capacity and service life of the gear reducer.

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